Casting is both an art and a science governed by numerous rules, or "laws." Personal interpretation of these laws is demonstrated in a technician's approach to the procedures involved in the art of casting. Integrating the theoretical principles supporting this process enables one to blend science with art in dental technology.
Success in fabricating metal ceramic crowns and fixed partial dentures depends to a large extent on obtaining high quality castings that are properly designed and well fitting.
One of the most common problems in casting results from heat distortion due to the limited number of shapes of casting rings currently available as well as the shortcomings in the construction composition of those presently available.
Our newly invented Horseshoe Shaped Casting Ring and Crucible Former addresses these common heat distortion problems.
In casting, the correct calculation of the geometric center and the heat center of the casting ring are critically important to achieve the best results. The center of mass (investment) may be different from the geometric center of the casting ring and consequently becomes the casting ring's true thermal zone. Correspondingly, the center of mass (molten alloy) can also become the heat center of the ring. As a result, the selection of a casting ring of sufficient length and diameter to accommodate the patterns to be invested is extremely critical. The casting ring should permit the patterns to be 7-mm apart and 7-mm from the top of the investment, with a minimum 19-mm of investment between them and the ring liner. Unless the basic laws are observed, mold fracture, casting fins, and shrinkage porosity is likely.
Previously, other means and methods for preparing castings and molds have been proposed using what is called a "lost wax" method. This method is well known in the dental field. Dental professionals are aware that casting must be undertaken with care and accuracy to produce a useful product with a precise fit.
The purpose of the crucible former is to allow for a uniform entry point to the sprue former and seal the casting ring at its base. Casting crucible formers are usually made of rubber, plastic, or silicone, which may or may not have a metal insert inside. To form a seal at the base of the casting ring, the crucible former must conform to the shape of the casting ring.
The purpose of the cradle is to hold and support the casting ring on the cradle carriage bars on the Centrifugal Casting Machine during rotation.
The purpose of the tong is for placement, retrieval, and transporting the heated casting ring to and from the worktable, oven, and the cradle on the centrifugal casting machine. The tong must be specifically designed to safely and effectively handle and transport the heated casting ring.
Another problem faced by dental laboratory technicians is the loss of valuable time related to the multiple casting procedures presently needed to fabricate multiple unit fixed partial dentures.
To our knowledge, no one has ever invented or produced anywhere in the world a Horseshoe Shaped Casting Ring, a Horseshoe Shaped Crucible Former, Cradle and Tong as depicted in our invention.
It is toward the resolution of those casting problems that have not been solved by prior art that our present invention is directed.